1. Field of the Invention
This invention relates to a resin composition having superior mechanical properties. More specifically, the invention relates to a resin composition having superior mechanical properties which comprises (A) a polymer obtained by ring-opening polymerization of (1) 5-cyano-bicyclo[2,2,1]-heptene-2 or a mixture thereof with a small amount of a cycloolefin-type compound in the presence of (2) an unsaturated polymer containing a carbon-carbon double bond in the molecule (to be referred to hereinafter as an "unsaturated polymer"), and (B) a homopolymer of vinyl chloride and/or a copolymer composed mainly of vinyl chloride (to be referred to hereinafter as a vinyl chloride-type polymer).
2. Description of the Prior Art
Vinyl chloride-type polymers are widely manufactured commercially and have a wide range of applications. It is widely known, however, that when these vinyl chloride-type polymers are fabricated into molded articles, their impact strength is not entirely satisfactory.
In order to improve the impact strength of vinyl chloride-type polymers, frequently the practice is to employ a grafting method wherein a vinyl chloride monomer is graft-copolymerized with a relatively large amount of an unsaturated polymer, and a blending method wherein a vinyl chloride-type polymer is blended with an unsaturated polymer. Although these grafting and blending methods can be used to improve the impact strength of vinyl chloride-type polymers, it is also widely known that the mechanical properties such as tensile strength and hardness and the thermal properties such as heat resistance of the product are reduced.
On the other hand, less deterioration in mechanical properties other than impact strength and in heat resistance occurs with resin compositions obtained by blending vinyl chloride-type polymers with impact-resistant resins such as a terpolymer of acrylonitrile/butadiene/styrene (ABS resin) or a terpolymer of methyl methacrylate/butadiene/styrene (MBS resin) than with compositions obtained by blending unsaturated polymers with vinyl chloride-type polymers but such polymers are not satisfactory from the viewpoint of increasing impact strength.
Thus, an improvement in the impact strength of vinyl chloride-type polymers can be achieved with compositions obtained by incorporating unsaturated polymers or impact-resistant resins in vinyl chloride-type polymers and with grafted products obtained by graft-copolymerizing vinyl chloride with unsaturated polymers, but these blends and products are not satisfactory because the superior properties of the vinyl chloride-type polymers, for example, mechanical properties such as tensile strength, rigidity and hardness, transparency, and heat resistance, are deteriorated.
Previously, it was found that a polymer obtained by ring-opening polymerization of 5-cyano-bicyclo[2,2,1]heptene-2 had various superior properties, and a process was suggested for its production [e.g., as disclosed in Japanese Pat. Publication No. 23720/75 (corresponding to U.S. Pat. No. 3,856,758) and U.S. Pat. application Ser. No. 714,833, filed Aug. 16, 1976].
Furthermore, it was found that a composition of superior quality was obtained by incorporating a ring-opened polymer of 5-cyano-bicyclo[2,2,1]heptene-2 obtained by the above-described method in a vinyl chloride-type polymer [e.g., as disclosed in Japanese Patent Application (OPI) No. 52246/74 (corresponding to U.S. Pat. No. 4,021,510)]. This composition has improved heat resistance and impact strength without a deterioration in the superior mechanical properties, such as tensile strength and hardness, and transparency of the vinyl chloride-type polymer, and therefore is better than the compositions described hereinabove. However, the improved impact strength of this composition is not entirely satisfactory from the viewpoint of practical applicability. Especially when such a composition is molded into articles requiring high impact strength (such as various machine component parts, automotive parts, window frames, helmets, and component parts of electric machinery and appliances), the impact strength of these molded articles is not sufficiently high.
It was further discovered that a composition having superior impact strength was obtained by incorporating an unsaturated polymer in a ring-opened polymer of 5-cyano-bicyclo[2,2,1]heptene-2 (e.g., as disclosed in Japanese Patent Application (OPI) No. 45853/75 and U.S. Pat. application Ser. No. 501,243, filed Aug. 28, 1974). Although this composition has improved impact strength, other mechanical properties such as tensile strength and hardness are deteriorated.
Investigations were thus made in order to obtain compositions having good impact strength and other mechanical properties. As a result, it was found that by incorporating an unsaturated polymer and a vinyl chloride-type polymer in this ring-opened polymer of 5-cyano-bicyclo[2,2,1]heptene-2, a composition having relatively good impact strength and heat resistance can be obtained (e.g., as disclosed in Japanese Pat. application (OPI) No. 14846/75). When the amount of the unsaturated polymer is relatively large, the impact strength of the composition is superior, but the other mechanical properties are deteriorated. On the other hand, when the proportion of the unsaturated polymer is relatively small, the mechanical properties such as tensile strength and hardness are good, but the composition is not satisfactory from the standpoint of improving impact strength.